Apologies for that. :/
Now we have a new key that expires in 5 years.
:r !wget -q http://debian.webconverger.com/archive-key.asc -O /dev/stdout | gpg pub 2048R/AB9E8DA9 2011-04-16 Webconverger Archive Automatic Signing Key <firstname.lastname@example.org> sub 2048R/B8E27CCA 2011-04-16 [expires: 2016-04-14]
The webconverger-archive-keyring package has been updated and so has the live-helper configuration.
This message comes from the London Hackspace.